Nowadays, high-quality power supplies with increasing energy efficiency are in high demand. Power factor correction technique plays an important role in improving the electric power supply efficiency of electric appliances, which are usually inductive loads that cause the current and voltage out of phase leading to low energy efficiency. A power factor corrector synchronizes the phases of the input voltage and the input current of an electric appliance, namely, the load of the electric appliance is adapted similar to a resistance-type load, thus harmonic distortion of the input current is effectively reduced resulting in high power factor of power supply.
A common power factor correction device requires a pulse width modulation (PWM) signal generator to provide a pulse width modulation (PWM) signal and a sample of an input voltage as a reference signal for correcting the current. In the conventional technologies, for example, the pulse width modulation signal generator disclosed by U.S. Pat. No. 5,886,586 does not require the input voltage sample but uses an integrator to perform one-cycle (i.e., feed-forward) control method to decide charge-discharge time and electric potential of an integrated capacitor. Other US patents, such as U.S. Pat. Nos. 7,068,016 and 5,804,950, also disclose similar technologies. However, the above patents using the integrator or the integrated capacitor in or out of a circuit, as such the response speed of the internal circuit is greatly reduced during the operation. In addition, the circuit is internally provided with a switch for discharging the integrated capacitor; therefore, power consumption is increased and the circuit space is enlarged.
Hence, the invention provides a power factor correction device and a correcting method thereof to solve the above problems.